Recently, LCDs that are light and thin and have low power consumption characteristics have been widely used in office automation equipment, video units and the like. However, unlike the display images of CRTs (cathode ray tubes) and EL (electroluminescence) devices, the display images of LCDs do not emit light themselves. Accordingly, a transmissive LCD (also known as a transmission LCD) is equipped with a backlight at a rear of a display screen thereof.
As shown in FIG. 4, a conventional transmission liquid crystal display 100 includes a first glass substrate 115, a second glass substrate 135 opposite to the first substrate 115, and a liquid crystal layer 120 interposed between the first and second substrates 115, 135. A front polarizer 111 and a front retardation film 113 are disposed on an outer surface of the first substrate 115, in that order from top to bottom. A front alignment film 119 and a common electrode 117 are disposed on an inner surface of the first substrate 115, in that order from bottom to top. A pixel electrode 137 is laminated on an inner surface of the second substrate 135. A rear alignment film 139 is laminated on the pixel electrode 137. A rear retardation film 133 and a rear polarizer 131 are disposed on an outer surface of the second substrate 135, in that order from top to bottom. A backlight module 104 is provided under the rear polarizer 131.
The front retardation film 113 and the rear retardation film 133 are quarter-wavelength plates. Liquid crystal molecules (not labeled) of the liquid crystal layer 120 are homogeneously aligned. An absorption axis of the front polarizer 111 is orthogonal to that of the rear polarizer 131, and the front retardation film 113 has a slow axis perpendicular to a slow axis of the rear retardation film 133. The slow axis of the front retardation film 113 maintains an angle of 45 degrees relative to the absorption axis of the front polarizer 111.
The liquid crystal layer 120, the common electrode 117, and the pixel electrode 137 cooperatively define a pixel region. When a voltage is applied to the transmission LCD 100 (as shown in FIG. 5), an electric field is generated between the common electrode 117 and the pixel electrode 137. The electric field can control the orientation of the liquid crystal molecules in the liquid crystal layer 120 in order to display images. Anchoring energy exists between the alignment films 119, 139 and certain of the liquid crystal molecules adjacent to the alignment films 119, 139. Therefore when an electrical field is applied, these liquid crystal molecules need an unduly long amount of time to become oriented according to the applied electrical field. This typically results in residual images being produced. In addition, liquid crystal molecules adjacent to the alignment films 119, 139 cannot be aligned to perpendicular to the first and the second substrate 115, 135, respectively. Thus light beams that have different incident angles and that transmit through the liquid crystal layer 120 produce different phase delays. This lowers the contrast of images displayed by the LCD 100, and also narrows the viewing angle of the LCD 100.
What is needed, therefore, is a liquid crystal display device which has a fast response time.